Simulation Study On Amorphization Of Ge₂Sb₂Te₅ Thin Films Induced By A Short Pulse Laser

With the rapid development of computer technology, the way that information stored changed, and optical storage technology(Phase-change storage) arises. People studied it by a lot of experiment methods and theoretical calculations, but the structure of amorphous and the reason of ultrafast phase-change were not clear. There are two main reasons for this: 1. The time of phase change is short; The area of phase change is small. 2. The theoretical calculations were based on the annealing process, the characteristics of laser-induced phase-change were not well performed. In order to solve these problems, this paper calculated the amorphization process of phase-change induced by laser using the first principle molecular dynamics calculation. And then the sub-structure and the electronic structure of amorphous Ge2Sb2Te5 were analyzed.First, the crystalline Ge2Sb2Te5 film was transformed to amorphous induced by laser. And then we got the temperature curve in the surface of the film using the finite element simulation software. The temperature curve was divided into four parts: heating stage, constant temperature stage, cooling stage, room temperature stage. Finally, we calculated the amorphization process using the first-principles molecular dynamics simulation software. K points was 2×2×2, the energy cut-off was 200 eV, the electronic interactive correlation function was generalized gradient approximation(GGA). Calculated by the first principle molecular dynamics, we obtained the amorphous structure and found that the energy of the crystalline and the amorphous structure were almost the same. These provided the energy foundation for the phase transition.The properties of the atomic structure and the electronic structure were studied by the first principle, and we also analyzed the mean square displacement(MSD), bond population, the charge density difference, the radial distribution function, bond length, bond angle, the band gap and the density of states. According to the atomic motion trajectory, we expounded the transformation mechanism of amorphization process. We found that Ge jumped into tetrahedral from octahedral caused by the vacancy, and then formed lot of four-fold rings in the amorphous structure. This demonstrates the importance of the vacancy. We speculated that the bond length did not need to change too much, were just distorted in the amorphization process.In this paper, the features of the amorphous Ge2Sb2Te5 were analyzed, and got the process of the phase-change, analyzed the importance of vacancies. It has not only made contribution to the mechanism of phase-change, but also the discovery of phase-change materials.